In light-emitting devices (e.g., light-emitting diodes (LEDs)) used recently, light extraction efficiency has become an important research issue in terms of energy efficiency.
Further, an energy conversion ratio in LED chips is about 15% or less, and the remaining 85% of electric energy is converted into thermal energy and consumed, so heat dissipation is very significant.
In order to solve a problem of heat dissipation, a thickness of a phosphor plate has been increased, thereby lowering light extraction efficiency.